The present invention relates to an automatic transmission fluid and particularly concerns an additive for such a fluid that will improve its stability against torque degradation while at the same time imparting suitable friction modification. The invention is also directed to additive concentrate packages that are intended for formulation into mineral oil base stocks preferably containing seal swellant to provide transmission fluids of improved stability against oxidative degradation.
A very high percentage of vehicles such as automobiles, tractors and earthmovers are now equipped with some type of semi-automatic or fully automatic transmission. These transmissions must be provided with a supply of fluid that serves the multiple functions of a power transmitting medium, a hydraulic control fluid, a heat transfer medium, and a satisfactory lubricant. A transmission fluid to be useful must be capable of operating over a wide temperature range, possess a high degree of oxidation resistance, be free of corrosive action, have foam control, have satisfactory low temperature fluidity, retain a useful viscosity at high temperatures, have transmission seal compatibility and lubricity without "stick-slip" of the transmission parts.
Exemplary of automatic transmission fluids are those disclosed in U.S. Pat. No. 3,410,801 which is directed to a class of modifiers of the friction characteristics of automatic transmission fluids (hereinafter designated ATF) to reduce squawk and chatter of the transmission; and U.S. Pat. No. 4,017,406 where the carboxylate half esters of 1-aza-3,7-dioxabicyclo[3,3,0]oct-5-yl methyl alcohols are taught in columns 13 and 14 to be useful friction modifiers for ATF.
In U.S. Pat. No. 3,248,187 C.sub.1 to C.sub.30 alkyl substituted acid lactones are taught to be useful as anticorrosion additive for lubricating oils and fuels, said acid lactones prepared by the acid catalytically induced lactonization of alkenyl succinic acid e.g. octadecenyl acid (see column 2, line 70).
The current approach to improving ATF is to adjust and modify the various additives so as to extend their useful lifetime. An additive, such as a friction modifier, which would operate as a functional additive while providing activity to limit the functional degradation of the ATF is desirable.
Recently published U.S. Pat. No. 4,062,786 teaches of chemical and oxidatively stable lactone oxazoline reaction products of hydrocarbon substituted lactone carboxylic acids, e.g. lactonized 2-octadecenyl succinic anhydride with a 2,2-disubstituted-2-amino-1-alkanol which are reported to be useful as sludge dispersants for lubricating oil or antirust agents for gasoline.